The U.S. government confirmed Friday that it has been holding an American-born journalist, who works in Iran, in jail since Sunday as a “material witness” in a case in federal court in Washington and that she will be released after she testifies before a grand jury.

No date was given for the testimony and no information about the nature of the case was revealed in a two-page court filing unsealed Friday.

Marzieh Hashemi, 59, has been a producer and on-air presenter for Press TV in Iran for 25 years. She is an American citizen, her family said. Press TV is an English-language network based in Tehran and overseen by the Iranian government.

Hashemi returns periodically to the United States to visit her family. She had been working on a documentary about Black Lives Matter in St. Louis, her family said, and was arrested on a material witness warrant by the FBI when she arrived at Lambert International Airport in St. Louis before a flight to Denver to visit her adult children. She was then transported to Washington and apparently is being held in the D.C. jail, her family said.

The FBI had declined to acknowledge the arrest until Friday and her court case is sealed. An unsealed court order Friday said Hashemi, who also is referred to in the filing by her birth name of Melanie Franklin, has not been accused of any crime.

Material witness warrants are rare. Hashemi’s case is the first such filed in federal court in Washington this year, and the court’s electronic docketing system indicates only two such cases were filed last year. Both are under seal.

Her son Hossein Hashemi, a research fellow at the University of Colorado, told The Washington Post Friday that he, his mother and two of his siblings had been subpoenaed to appear at U.S. District Court in Washington, but said he did not know the subject matter. He said that neither his mother nor any of his family had testified and that “we don’t anticipate her getting out today.”

“She’s been very critical of certain official policies the U.S. has taken,” Hossein Hashemi said, “both domestically and internationally. We don’t think any of that should lead to her arrest.” He said his mother would have cooperated with the FBI if they had simply asked to question her.

Hashemi’s attorney, Preston Burton, said, “Marzieh Hashemi’s perseverance has been remarkable in the midst of difficult circumstances, and it is my privilege to represent her. She is heartened by the many expressions of concern about her well-being, and we expect that she will soon return to her family, her home and her career.”

Press TV said Hashemi was being treated disrespectfully by American authorities, who reportedly removed her headwear and fed her pork, which are banned in the Muslim religion. Hashemi converted to the Muslim faith and moved to Iran decades ago, Press TV said.

On Friday, the Justice Department released an order signed by Beryl Howell, chief judge for the federal court for the District of Columbia. Howell’s order said Hashemi had been arrested on a material witness warrant issued by a district court judge in Washington and she had been appointed an attorney.

Howell’s order said Hashemi had made two court appearances before a judge while represented by counsel. The judge said the government expected to release her “immediately following the completion of her testimony before a grand jury investigating violations of U.S. criminal law.” Grand jurors met Friday, although it was not immediately clear whether Hashemi testified or completed her testimony.

The order does not specify which office in the Justice Department is involved in the case being investigated.

Hashemi was at the courthouse Friday, as were several family members.

Material witness warrants were used to detain possible witnesses or suspects after the 9/11 terrorist attacks, and witnesses were often released soon after their testimony was heard. But an analysis by Human Rights Watch and the American Civil Liberties Union in 2005 found that the government had held 70 men as potential witnesses and nearly half were never called to testify.

The report concluded the use of the warrants was excessive and frequently unlawful because many detainees were never questioned by a grand jury or were denied access to attorneys for extended periods of time. Most were never charged with a crime, the report found.

Last week, Iran confirmed it is holding U.S. Navy veteran Michael R. White at a prison, making him the first American known to be detained there under President Trump’s administration, according to the Associated Press.

At least four other American citizens are being held in Iran.

The AP report also said Iranian Foreign Ministry spokesman Bahram Ghasemi told state TV that Hashemi’s arrest indicates the “apartheid and racist policy” of the Trump administration. “We hope that the innocent person will be released without any condition,” Ghasemi said.